Sticking professionals: gecko and
mussel; © Northwestern University
Mussels are a thorn in ship owners‘ flesh. That is due to the fact that they love to stick on underwater hulls which slows down speed and rises fuel costs. To remove the stowaways is difficult and expensive as they stick bomb-proof. In their natural environment they have to defy salt water, current and heavy surf.
In this case, the captain’s poison is the chemist’s meat: Klaus Rischka is a postdoctoral research fellow at the Fraunhofer Institute for Manufacturing Technology and Applied Materials Research in Bremen. The chemist and his colleagues are interested in mussel glue, „since it will stick solidly even if it is wet”. Probably, it can also be degraded by body’s own scavenger cells. This would be ideal for medical applications, for example for fixing dental implants, artificial heart valves or stents.
Instead of suturing surgical wounds or organs, these may be fixed with mussel adhesive in future. A new and promising approach, if it works: on the one hand big surfaces can be connected faster by glueing; on the other hand glue allows working in tiny dimensions. “Surgeons cannot suture as small as they like. This is especially problematic in microsurgery”, Rischka explains.
The aim is to produce a synthetic adhesive in the style of mussel glue because the natural one, which is made by the mussel’s gland, is costly. “10.000 mussels produce only one gram adhesive”, says Rischka. This is very expensive and eco-unfriendly at the same time. Moreover, the material must have a constant quality if it is used for medical applications, “but natural products are often contaminated by impurities”.
The researchers have produced some peptide units so far which are single components of the mussel adhesive. However, the new adhesive will come out in five years at the earliest, Rischka believes.
Geckos: Sticking Without Adhesive
Also geckos have sensational sticking skills. They run over windows and hang headfirst on the ceiling without any problem. The American biologist Kellar Autumn lifted the secret of this phenomenon seven years ago: There are millions of very fine hairs under each gecko foot. More contact points between hairs and surface result in a significant increase in adhesion force.
Exactly this strategy serves as a model for a new medical adhesive tape. Researchers of the American Massachusetts Institute of Technology (MIT) have imitated the gecko hairs by putting their liquid, new developed plastic on a perforated silicon surface. After the plastic had been hardened, the film was taken off. “Hereby, numerous small hairs were arising on the surface”, explains the Swiss chemist Andreas Zumbühl, who was involved in the development.
However, the adhesive tape does not stick in a wet environment. To solve this problem the tape is coated with a sugar polymer consisting of some hydroxyl groups. These are able to bind water via electrostatic forces, so called hydrogen bonds. Furthermore, the polymer contains aldehydes which can link to amines situated on the cell’s surface. Thanks to the gluey substance the tape is able to stick till the wound is healed. “Currently, my colleagues are trying to imitate the gecko hairs even better in order to increase the adhesive force of our tape”, Zumbühl says.
Gecko and Mussel: In Conjunction Unbeatable
Researchers of the American Northwestern University in Illinois have recently had the idea to combine the adhesive strategies of gecko and mussel. They imitated a gecko’s foot by nanofabricating arrays of silicone pillars and coated the pillars with a very thin layer of a synthetic polymer that mimics the wet adhesive mussel proteins. That way they developed a new adhesive tape which is called “geckel” – a neologism of “gecko” and “mussel”.
Zumbühl believes:“However, due to its enormous elasticity our adhesive tape is more suitable for medical applications than geckel”. The plastic is stretchable to double size. Thereby it is possible to patch for example a whole in the heart as the tape matches with its movement.
„To use the mussel adhesive is indeed a peach of an idea”, Zumbühl admits, as it sticks much better than the sugar polymer. “Probably, a synthesis of both, of our plastic and the mussel adhesive, would be ideal. One should try that, immediately.”